The overall purpose of this project is to investigate the role of liver macrophages, or Kupffer cells (KC), in resistance to intracellular pathogens. KC line the sinusoids of the liver, and consequently clear the blood of gastrointestinal and other blood borne pathogens. KC appear to have an important role in the early events in host resistance to many pathogens. For a number of years, we have studied a prototypic model of intracellular infection, murine listeriosis. Host defenses in this model depend on the interaction between T lymphocytes and macrophages. For the past three year grant period, we have developed and used T cell clones to investigate the role of T cells in immunity to Listeria. Most recently, we have developed techniques for isolating KC from livers. In an initial study, we found that KC can serve as efficient antigen-presenting cells to Listeria-specific T cell clones in vitro, thus demonstrating the potential of KC to initiate an immune response. In this proposal, we will study two major functions of KC and the capacity of T cells to regulate these functions during listerial infection. Initially, we will measure the production of cytokines, including interleukin-1, interleukin-6, and interferon, by KC during listeriosis. KC cytokine production will be determine in vivo by Northern blot analysis, in situ hybridization, and immunohistochemistry. These studies will be confirmed by in vitro analysis of cytokine production by isolated KC populations. The factors that regulate cytokine production by KC will be identified by both in vivo and in vitro studies. In addition, the antimicrobial potential of KC will be determined by analyzing in vivo growth curves of KC-associated Listeria. To confirm in vivo studies, we will measure the capacity of KC harvested from infected mice to kill Listeria in vitro. We will also use well established assays to investigate the capacity of KC to kill Listeria in vitro after stimulation with T cells and T cell products. By investigating secretory and antimicrobial activity of KC during listeriosis, we hope to define the importance of KC during murine listeriosis. These studies will be the first to study comprehensively the role of KC in the immune responses to infection. Immune mechanisms active in listeriosis have proven to have wide applicability to immune host resistance against many pathogens. The findings from our studies, therefore, will advance our understanding of immunity against infection in general, and may lead to newer approaches to enhance immune host defenses.